Page:Popular Science Monthly Volume 12.djvu/583

This page has been validated.

the speaker at the other end could be distinguished so long as silence was maintained in the room, or so long as no heavy lorry rumbling over the stones outside sent in harsh noises which drowned the faint whisper of the instrument. The resistance was gradually raised to 4,000 ohms nearly—300 miles—with like favorable results; and for some little distance beyond, articulation could still be made out. But, by the time 10,000 ohms had been applied, putting the speaker at a distance of, say, 700 miles, sound only, but not articulate sound, reached the ear. The tone was there, and every inflection of the voice could be followed; but articulation was absent, although the listener strained every nerve to catch the sound, which the speaker, as

PSM V12 D583 Bell telephone in use.jpg
Fig. 8.

was afterward ascertained, was shouting in a loud, clear voice. The prolonged notes of an air sung could be heard with the resistance named, but again no words could be distinguished."

The next experiment was to join up the telephones in the office with different line-wires in succession going to various distances, and working with different kinds of telegraph-instruments. "When this was done, the real obstacle to telephonic progress at once asserted itself in the shape of 'induction.' The first wire experimented with was partly 'overhouse' and partly underground, and the offices upon it were working A B C, or printing-instruments. It is difficult to render clear to the person ignorant of telegraphic phenomena the idea